1. Field
Methods and apparatuses consistent with the exemplary embodiments relate to a method and an apparatus for mapping a quadrature amplitude modulation (QAM) symbol, and more particularly, to mapping a QAM symbol by categorizing and mapping data based on magnitudes of frequencies of carrier signals.
2. Description of the Related Art
Due to the developments in electronic and communication technologies, digital technologies have been introduced to broadcasting system industries, and various digital broadcasting formats are being suggested. From among these formats, a multi-carrier signal system employed by a digital video broadcast-terrestrial (DVB-T) format is an orthogonal frequency digital multiplexing (OFDM) system. The OFDM is a technology employed as the standards of IEEE 802.11a, ETSI BRAN'S HYPERLAN2, European digital TV broadcasting DAB, and DVB-T. In the related art single-carrier signal system for transmitting data via a single carrier signal, intense interference occurs between symbols, which increases distortion. Therefore, it is necessary to increase the complexity of an equalizer at the reception end. To resolve such problems of the single-carrier signal system, the OFDM system has been introduced.
The OFDM system is a system for transmitting data via multi-carrier signals by parallel-converting data symbols input in series, modulating each of the parallel-converted data symbols to a plurality of mutually orthogonal tone signals, and transmitting the tone signals.
Compared to the related art multi-carrier signal system, orthogonality is maintained between surrounding tone signals in the OFDM system. Therefore, optical transmission efficiency may be acquired during high-speed data transmission. Furthermore, the OFDM system features high efficiency of using frequency and is strong against multi-path fading.
In the OFDM system, OFDM symbols are transmitted in various transmission units, e.g., frames or super-frames. Each OFDM symbol includes a plurality of symbols. Each symbol may indicate at least one or more data bits.
Wired communication technology is generally used in the fields including telephone, cable TV, internet access, and optical communication. Compared to the past, high-quality image data and high volume data are increasing, and techniques for transmitting such data are being developed.
In a case where a common 128 QAM constellation is used in the related art 10 Gbase Ethernet, since distances between symbols are not uniform, only 128 symbols are arranged in a region used by 256 QAM constellation to unify and increase distances between symbols. As a result, only 50% of the region is actually used, and transmission efficiency is deteriorated.
Furthermore, in a case of wired communication, if high frequency signals are used for transmitting a large amount of data, signal reduction is significant.